mailmap: avoid out-of-bounds memory access

AddressSanitizer (http://clang.llvm.org/docs/AddressSanitizer.html)
complains of a one-byte buffer underflow in parse_name_and_email() while
running the test suite. And indeed, if one of the lines in the mailmap
begins with '<', we dereference the address just before the beginning of
the buffer when looking for whitespace to remove, before checking that
we aren't going too far.

So reverse the order of the tests to make sure that we don't read
outside the buffer.
Signed-off-by: NRomain Francoise <romain@orebokech.com>
Signed-off-by: NJeff King <peff@peff.net>

mailmap.c

@@ -118,7 +118,7 @@ static char *parse_name_and_email(char *buffer, char **name,
 	while (isspace(*nstart) && nstart < left)
 		++nstart;
 	nend = left-1;
-	while (isspace(*nend) && nend > nstart)
+	while (nend > nstart && isspace(*nend))
 		--nend;
 
 	*name = (nstart < nend ? nstart : NULL);